The present invention concerns a force and movement conversion mechanism which in piston machines with at least one piston is used for transmitting forces between the reciprocating piston/pistons in the machine and its rotating power input or power output shaft depending on the application of the machine.
More precisely the invention concerns a piston machine comprising at least one axially movable piston in a cylinder, the piston being connected to a rotating power input or power output shaft through a preferably hollow and cylindrical piston-rod which is connected to a crosshead yoke disposed perpendicularly to the piston-rod axis, in which crosshead yoke two crosshead slides are disposed on each their crank pin journal and fitted in between sliding surfaces formed in the crosshead yoke, where they synchronized are forced to perform sliding along the yoke in mutual perfect opposition, as the two crank pin discs or double cranks interacting via yoke are forced to rotate with identical rpm in mutual opposite direction of rotation and adjusted in such a way that the two crosshead slides on exact same time are situated in the positions in the yoke, where the piston is in its top or bottom dead point.
The mechanism may be used in piston machines with either crank pin or crank mechanisms, like the hitherto known xe2x80x9cScottish Yoke Mechanismxe2x80x9d, it uses a crosshead yoke disposed perpendicularly to the central axis of the piston, but deviates from xe2x80x9cScottish Yoke Mechanismxe2x80x9d by using two, instead of one, crosshead slides placed on crank pin journals performing their sliding movements longitudinally of the crosshead yoke in mutual opposite direction with decelerations and accelerations which at any time are identical for both crosshead slides, and as they reverse their sliding direction on the exact same time, which is achieved by using a synchronizing mechanism suitable for this ensuring that the utilized crank pin discs or crank shafts, two for one crosshead yoke, the journals of which are suspended in the bearing bushing of their individual crosshead slides, are rotated with the same rpm about their central axes extending perpendicularly to the longitudinal direction of the yoke, but in mutual opposite direction of rotation, as the synchronization, besides that, is adjusted in such a way that the two crosshead slides on the exact same time are situated exactly in the position in the crosshead yoke causing the piston to stand in its top dead point position or bottom dead point position.
A piston machine as disclosed by way of introduction is known from SU-A-1,281,700. This document discloses a piston engine with a piston rod connected to a single crosshead yoke, the yoke is connected to two crank shafts rotating at the same rpm in opposite directions. The connection to the yoke is provided by crosshead slides fastened to the yoke so that the crank shafts and the piston reach top and bottom dead center at exactly the same time, in synchronism.
Thus the piston machine discloses a construction with two parallel crank shafts being connected to a single piston through the yoke mechanism. Each crosshead slide is provided as a glide bushing and a further bearing bushing which is arranged perpendicularly is used for the connection to the crank shaft journal. This construction is rather complicated and associated with drawbacks as the centre line of the crosshead slides should be displaced in relation to the centre line passing through the central lines of the two co-operating crank shafts when these is provided in same distance at each side of the piston axes. This construction makes it necessary to have a rather large height of the machine and moreover, the length of different piston rods would be different from each other. Moreover, the construction with one or two set of pistons arranged in the central part of the yoke is inconvenient as the yoke hereby is subjected to bending in the longitudinal direction.
It is the object of the present invention to disclose a piston machine which do not suffer from the drawbacks associated with prior art piston machines and which may be used in connection with a power input or a power output shaft depending on the application of the machine, which machine simultaneously is able to work with a yoke mechanism embodied as an I-yoke or a beam yoke and which piston machine could have the power input or power output shaft provided in the form of a crankshaft or the shaft for a crank pin disc.
According to the present invention this object is obtained with a piston machine mentioned by way of introduction and being characterised in that the yoke is provided with top and bottom flanges, which at their mutually facing side surfaces form longitudinal sliding surfaces, or are basis of fastening of longitudinal sliding surfaces fastened thereon, wherebetween the two crosshead slides at each side of the web part of the yoke in mutual opposition perform their sliding movements along the yoke, as they at the middle of this pass each other and perform outward strokes, which for both slides at the exact same time is finished by their turning of their direction of sliding equidistantly from the middle of the yoke, where pistons at their piston-rods are fastened on the outward facing side surface of the top flange and/or bottom flange of the yoke, and that the pistons thereby are arranged directly over the associated power input or power output shaft.
With the movement of the crosshead slides it is possible to have the piston axes arranged directly over the shaft used for power input or power output when the pistons are arranged in their top and bottom dead center. Hereby no bending action will occur in the yoke. Simultaneously, the yoke construction may be embodied as a technically simple product as the sliding surfaces maybe provided by web parts of a beam which may have different embodiments.
The invention is thus suitably effected by using in principle two different shapes of crosshead yokes, of which one is particularly suitable for using together with crank pin discs, it has a mainly I-shaped cross-section why the yoke subsequently is designated xe2x80x9cI-yokexe2x80x9d, while the mechanism of which it forms a part is designated xe2x80x9cI-yoke mechanismxe2x80x9d, the other crosshead yoke is especially suitable for use together with crank-shafts, it is built up by interaction between two so-called sliding surface beams, why the yoke subsequently is designated xe2x80x9cbeam yokexe2x80x9d, while the mechanism of which it forms a part is designated xe2x80x9cbeam yoke mechanismxe2x80x9d.
As the pistons reach their top or bottom dead points simultaneously, then their sliding in each their direction perform decelerations which at every time are identical for both crosshead slides and is continued until they after 90 degrees of rotation of the crank pin discs or cranks on the exact same time turn the direction of movement of their sliding stroke and herefrom quite uniformly are accelerated up to their greatest sliding speed, which is achieved just at the passage of their position in the yoke at the subsequent piston turning at its top or bottom dead point Accordingly, the impacts on the yoke are minimized.
The invention will be further explained in connection with the enclosed drawing.
The fundamental construction of the I-yoke mechanism appears on FIG. 1. The crosshead yoke (5) is an I-yoke made e.g. by sintering a light and strong alloy and formed in one with a not shown piston bolt fitting (48,48xe2x80x2 FIGS. 14 and 15) on which the piston-rods (2,2xe2x80x2) with their respective pistons are fastened.
At each side of the central web part (17) of the I-yoke, on the sliding surfaces (6,6xe2x80x2) between the top and bottom flanges of the I-yoke, there is inserted crosshead slides (14,14xe2x80x2), of which only one (14) can be seen. The rectangular sliding surfaces are intended to be coated with a smooth and wear-resistant material, e.g. amorphous diamond, besides that the crosshead slides are made with lubricating ducts extended to both the bushings and the sliding surfaces of the crossheads.